Micro-components, such as, but not limited to, microelectronic, micro-optoelectronic, and microelectromechanical systems (MEMS), share a common fabrication technology comprising the use of a substrate from which the micro-component is formed referred to as a die. Various techniques, such as layering, doping, masking, and etching, are used to build thousands and even millions of microscopic devices on and from the substrate. For example, a microelectronic die may have integrated circuit (IC) devices in the form of transistors, resistors, and others. The IC devices are interconnected to define a specific electronic circuit that performs a specific function, such as the function of a microprocessor or a computer memory.
Commonly, a plurality of die are simultaneously formed on a single substrate and subsequently separated into individual die. Examples of substrates include, among others, wafers comprising silicon (Si), gallium arsenide (GaAs), Indium Phosphate (InP), and their derivations. The die 2 are commonly formed on a die side 4 opposite a base side 5 of the substrate 1 in an array of horizontal and vertical rows, as shown in a perspective view in FIG. 1. An active area 3 is the portion of the die 2 that contains the micro-components. The active areas 3 are separated by streets 6. It is along the streets 6 that the die 2 are separated at some point in the fabrication process. The width of the streets 6 depends, in part, on the substrate material, further handling constraints, and the particular separation process used to separate, or singulate, the dice 2.
A number of methods are used to singulate each die 2. In one method, the dice 2 are separated from the substrate 1 by a process referred generally as sawing. Sawing involves the use of mechanical abrasion and/or erosion of the substrate 1 along the streets 6. Sawing may be achieved using a saw blade 10 driven by a rotary saw 9 (as illustrated in FIG. 2), or other techniques such as a vibrating stylus with a sharpened tip (not shown). The base side 5 of the substrate 1 is commonly mounted to dicing tape 7 having adhesive layer 8 to hold the dice 2 as they are being sawed to prevent die fly-away, as shown in cross-section in FIG. 3. The dicing tape 7 is commonly mounted to a saw frame (not shown). Sawing commonly is a two step process of providing a pre-cut 16 into the die side 4 and subsequently a through-cut 17, as shown as a cross-sectional exploded view in FIG. 4.
Sawing requires substantial post-separation processing to restore the dice 2 to a specified state of cleanliness. The act of sawing produces substantial debris which includes small pieces of the substrate 1 and possibly small pieces of the sawing implement, such as the saw blade 10 or vibrating tip. Also, the adhesive layer 8 must be removed from the base side 5. Cooling/lubricating fluid is another source of contamination. Special precautions, sometimes involving substantial processing steps, are commonly used to clean the singulated dice 2 and/or to protect the active area 3 before the sawing process. MEMS devices are particularly vulnerable to contamination as they incorporate mechanical components.
Another method used to singulate the dice 2 involves using a focused beam 15 from a laser 11 to ablate through the substrate 1 along the streets 6, as shown in FIG. 2. A beam 12 from the laser 11 is processed using mirrors 13 and lenses 14 to concentrate and position the focused beam 15. Issues, such as those related to the buildup of heat and process complexity and control, must be addressed.
Another method used to singulate the dice 2 involves a combination of grooving the active side 4 and fracturing through the thickness of the substrate 1 along a groove 18. Grooving refers to any process in which the streets 6, usually the die side 4, are provided with a groove 18 having a predetermined depth into the thickness of the substrate 1, as shown in FIGS. 2 and 3. Grooving is commonly done using a method such as sawing, such as with a pre-cut 16, using a laser 11, and scratching or scribing using a pointed stylus, among others. Commonly, the substrate 1 is mounted with dicing tape 7 to a saw frame (not shown).
A number of fracture methods are used to break the substrate 1 along the grooves 18. In one method, while mounted in the saw frame and provided on the dicing tape 7, the substrate 1 is caused to form fractures 19 by urging the base side 5 against a cylinder to flex or bow the substrate 1 to initiate fracture from the grooves 18 (FIGS. 3 and 4). The grooves 18 provide a point of crack initiation to form the fracture 19 that extend through the substrate 1.
In some of the current fracture methods, the substrate 1 must be removed from the saw frame in order to urge the substrate 1 against the cylinder. This removal from the saw frame and the actual fracturing of the substrate 1 is difficult to provide in an automated production process, leading to inefficiencies, longer lead times, and added cost.
As the drive for smaller and thinner die 2 continues, substrate 1 and corresponding active and passive device layers on and within the substrate 1 are being made thinner. For example, materials having a low dielectric constant (k) that can be made very thin are being investigated for use as inter-level dielectric (ILD) material. As the k is lowered, the ILD can be made thinner for the same electrical performance as one that is thicker with a higher k. The resulting smaller and thinner dice 1 are especially prone to die fly-off from the dicing tape 7 during singulation due, in part, to the decreased surface area of the smaller die 1 available to adhere to the dicing tape 7. Die fly-off causes high die yield loss and damage to the dicing equipment.
Further, the increased fragility of the thinner, low-k ILD requires more prudent handling to prevent unintentional fracture, cracking, and delamination, that can be caused by the current singulation methods.